In the related art, pulverized coal obtained by loading raw coal into a roller mill is used as fuel in a coal fired boiler. In the interior of the roller mill, the raw coal is milled into powder, and the milled pulverized coal is dried, classified, and convey on the air current through a pulverized coal tube installed on the top of the roller mill to a boiler by primary air.
FIG. 5 shows an example of configuration of the pulverized coal fired boiler. In this boiler, four roller mills 10 are installed for a furnace 1 having a rectangular cross section. Each of the roller mills 10 is connected to the furnace 1 by four independent pulverized coal tubes 2, and the pulverized coal as fuel is supplied to each wall surface of the furnace 1 through the air current conveyance. The four roller mills 10 each supply pulverized coal to the wall surfaces at different heights.
An example of configuration of the roller mill 10 will be described in brief according to FIG. 6 and FIG. 7.
The roller mill 10 in the drawing is an apparatus for milling raw coal loaded into the mill body 11 between a rotary table 12 and rollers 13, and supplying the pulverized coal (powder) having a predetermined grain diameter or smaller one separated by a rotary classifier 20 to the furnace 1 through the air current conveyance. There are provided three such rollers 13 at regular pitches circumferentially of the rotary table 12, and are turned with the upper surface of the rotary table 12 in association with the rotation thereof.
Opening on the top of the mill body 11 are fine particle exits 14 for discharging the pulverized coal classified by the rotary classifier 20 outside through the air current conveyance. The fine particle exits 14 open in a state of being circumferentially quartered, and the above-described pulverized coal tubes 2 are connected to the fine particle exits 14 individually. In other words, the rotary classifier 20 has the circumferentially quartered fine particle exits 14 opened on the top thereof.
Reference numeral 15 in the drawing designates a raw coal adding tube which penetrates through the center of axis of the rotary classifier 20, and reference numeral 16 designates an air-supply pipe which supplies primary air for the air current conveyance into the mill body 11. The primary air supplied to the interior of the mill body 11 through the air-supply pipe 16 flows out from air outlet 17 provided on an outer peripheral portion of the rotary table 12 into the interior of the mill body 11 to convey the pulverized coal.
Reference numeral 18 in the drawing designates a vane, and the vane 18 has a function to introduce air current in the mill body 11 in the direction of axial center thereof to provide a rotation.
As a technical literature relating to the roller mill for milling coal in the related art, there is the one in which a technology to achieve accurate distribution by disposing a guide panel at each exits to vary the quantity of the pulverized coal in association with variation in air quantity, since the air quantity varies with the change of a damper of the mill exit pipe for conveying the pulverized coal on the air current is disclosed (for example, see Patent Citation 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. HEI10-57828 (see FIG. 1 and FIG. 4)